In a charged particle beam exposure apparatus which performs exposure by causing a charged particle beam to form an image on a substrate, when the current of the charged particle beam is large, the image of the charged particle beam projected on the substrate is blurred by the Coulomb effect. Although most of the blur caused by the Coulomb effect can be corrected by readjusting the focal position of a reduction electron optical system for charged particle beam projection, an uncorrected blur component remains. Conventionally, the blur to be caused by the Coulomb effect is predicted on the basis of the area of the charged particle beam and apparatus parameters (the current density, the incident half angle of the charged particle beam, the acceleration voltage of the charged particle beam, and the optical length of the reduction electron optical system). The focal point of the reduction electron optical system is adjusted in accordance with the prediction result.
The Coulomb effect not only causes a blur in the image of the charged particle beam but also displaces the position of the image of the charged particle beam on the substrate. The displacement amount of the position changes in accordance with the shape of the charged particle beam and total current. In a multi-type charged particle beam exposure apparatus which draws a pattern by scanning a plurality of charged particle beams, the positional relationship among the charged particle beams changes in accordance with the distribution of the charged particle beams during drawing. FIGS. 22A to 22C show examples of this change.
Referring to FIGS. 22A to 22C, black dots denote charged particle beams on the substrate, and gratings indicated by broken lines are gratings determined by the designed positions of the charged particle beams. When FIGS. 22A and 22B are compared, the distribution of the charged particle beams on the substrate is uniform in both FIGS. 22A and 22B, but in FIG. 22B, the number of charged particle beams is larger (that is, the total current is larger), so the positional relationship among the charged particle beams changes more largely. When FIGS. 22B and 22C are compared, the distribution of the charged particle beams is not uniform in FIG. 22C (that is, anisotropic), so the gratings to be determined by the actual charged particle beams also change anisotropically. In this manner, when the positional relationship among the charged particle beams changes, the connecting precision among patterns drawn by the respective charged particle beams degrades, and a desired pattern cannot be formed at high precision. In other words, as the distribution of the plurality of charged particle beams changes during drawing in accordance with the density of the pattern, the influence of the Coulomb effect (a change in image position) when drawing a pattern with a large density differs from the influence of the Coulomb effect when drawing a pattern with a small density. Thus, when a pattern including a pattern with a high density and a pattern with a low density is to be drawn, the connecting precision among the patterns degrades.